Tiling over tiles – avoiding the unknown

Some people will tile over existing tiles to avoid the potential ‘problems’ listed in my article preparing walls for tiling and to save money on labour and disposal costs.

It tends to happen with cash strapped DIY renovations where there is a small budget, and buy to let properties where the landlord doesn’t think it necessary to spend the money on surface preparation.

I never do it in my professional Leeds based bathroom installation business due to liability issues and the fact that I base my reputation on doing things properly.

The biggest risks when tiling over existing tiles are:

1. it can look untidy / unprofessional
2. it can lead to your tiles falling off the walls

Although new tiles will normally stick or ‘bond’ to old tiles quite well in most instances (see tips below) you may well be ‘building a house on dodgy foundations’ by tiling onto an unsuitable substrate. This could lead to the new tiles pulling the old tiles from the wall beneath them.

Put simply, you are not just dependent on the bond between the new and old tiles, but on the bond between the old tiles and the substrate behind them (e.g. the render) and the bond strength between the render and the wall behind.

If the rendered walls beneath the existing tiles are blown (i.e. coming away from the wall), then adding the weight of new tiles will probably lead to both the new and old tiles and render falling away from the brick or blockwork wall behind – Lots of hard work ruined!

In this example, the ‘new’ tiles did not bond effectively to the existing tiles underneath, as they had been painted over with an unsuitable paint – this paint simply peeled off the glazed face of the existing tile, causing the new tiles to fall off the wall.

The alternative is to consult my article preparing walls for tiling and do the job to a professional standard. Consider the extra money needed to do the job properly as a long term investment, and as a way to mitigate risk and guarantee the longevity of your installation.

• Ensure existing tiles are strongly bonded to the wall behind – a hollow sound when tapped may indicate blown tiles (more common around wet areas).
• Ensure tile surfaces are clean and free from dust, grease or contaminants by using sugar soap to clean them – this will aid adhesion of the new tiles.
• Use the correct adhesive – check with the manufacturer that it can be used for tiling on tile or apply a small sample and allow it to set. If it’s very difficult to chip off then a good bond has been created. Flexible rapidset adhesive is best in my experience.
• Be aware that wall substrates have a maximum weight they can carry:
• Plaster 20kg/m2
• Plasterboard 32kg/m2
• If this is exceeded by adding (larger, thicker, heavier) tiles, the wall may fail i.e.the plaster / render could fall off it, bringing the tiles with it.
• Consider aesthetics – Double tiling will be noticeable around door frames and along tile perimeters if the room is only half tiled – You may also have difficulties getting a tile trim to fit.
• Consider practicalities – Double tiling may also stop bath taps from being able to be turned on and necessitate the moving of radiator pipes (as the radiator mounted on the wall will be pushed out into the room by the depth of the new tiles) for example.

If you have any questions, then feel free to contact me.

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